The present invention relates to a protecting tube for external cable applicable to a bridge or the like. More particularly, the present invention relates to a transparent protecting tube for external cable that is adapted to accommodate a tendon for prestressed concrete (hereinafter occasionally referred to simply as xe2x80x9ctendonxe2x80x9d) and filled with a filler.
External cables used for bridges or the like generally use protecting tubes for accommodating tendons. In such a protecting tube for external cable, a filler is tightly filled around the tendon accommodated therein, thereby preventing corrosion of the tendon.
Thus, the protecting tube for external cable needs to be filled tightly with a filler. Therefore, it is preferable that the protecting tube should allow visual observation of the filling condition of the filler. In addition, the protecting tube needs to withstand the filling pressure of the filler.
Japanese Patent Application Unexamined Publication (KOKAI) No. 2000-320071 discloses a tendon-protecting synthetic resin tube which is a transparent synthetic resin tube adapted to contain a tendon and filled with a filler. The synthetic resin tube has a flexible portion and a rigid portion that are formed from a polyvinyl chloride resin. The flexible portion is made of a polyvinyl chloride resin containing from 20 to 40 parts of a plasticizer. This document states that the synthetic resin tube is formed by spirally winding a belt-shaped flexible synthetic resin material in the longitudinal direction of the tube, the belt-shaped flexible synthetic resin material containing the rigid portion as a core material. It is also stated that the tendon is made up of prestressing steel wires or steel strands and used as a tendon for external-cable post-tensioning system.
In this synthetic resin tube, however, the plasticizer contained in the flexible portion in a large quantity migrates and causes the degree of flexibility to lower as time elapses. Moreover, because the synthetic resin tube uses a polyvinyl chloride resin, which is readily deteriorated by ultraviolet radiation or the like, it is difficult to increase durability. It is also feared that dioxin may be generated.
Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 9-144210 discloses a protecting tube for covering and protecting tendons, such as prestressing steel wires, steel strands or steel bars, used for prestressed concrete. The protecting tube has spirally corrugated inner and outer surfaces, and the whole of the tube is formed from a polyolefin resin material. The use of a high-density polyethylene resin is also stated in this document.
However, the tube which is spirally corrugated on both faces (i.e. protecting tube for a tendon, inner and outer surfaces of which are both spirally corrugated) exhibits low pressure resistance in the radial direction when it is filled with a filler. Moreover, the transparency of the tube lowers. Therefore, the filling condition of the filler in the tube cannot visually be confirmed with high accuracy.
Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 6-55636 discloses a cross-linked tube formed from a resin composition consisting essentially of an ionomer resin. The ionomer resin contains from 0 to 50 parts by weight of an ionomer resin in which the molecules of a copolymer of ethylene with (meth)acrylic acid have been crosslinked with sodium ions or/and zinc ions with respect to 100 parts of an ionomer resin in which the molecules of a copolymer of ethylene with (meth)acrylic acid have been crosslinked with potassium ions. The crosslinked tube is obtained by a method wherein the resin material is formed into a tube-like shape from an extruder and thereafter irradiated with an electron beam. The crosslinked tube is free from Lichtenberg discharge marks. This document also states that an adhesive or pressure-sensitive adhesive layer of an ethylene-ethyl acrylate-carbon monoxide copolymer is formed on the inner surface of the crosslinked tube.
However, because crosslinking is irreversibly effected by electron beam irradiation, the ionomer resin material cannot be reused. Moreover, it is difficult to improve pressure resistance.
Accordingly, an object of the present invention is to provide a cable protecting tube having high transparency and allowing the filling condition of a filler therein to be visually observed from the outside as well as exhibiting high pressure resistance.
Another object of the present invention is to provide a cable protecting tube that is excellent in low-temperature resistance, flexibility and durability and useful for accommodating a tendon and for filling with a filler to obtain an external cable.
As the result of conducting exhaustive studies, the present inventors found that the above-described problem can be solved by forming the cable protecting tube from an ionomer resin and reinforcing it, and made the present invention on the basis of this finding.
That is, the transparent protecting tube for external cable (hereinafter occasionally referred to simply as xe2x80x9cprotecting tubexe2x80x9d) according to the present invention is a transparent synthetic resin tube for accommodating a tendon and for filling with a filler. The transparent synthetic resin tube comprises a protecting tube formed from an ionomer resin and a spiral or mesh-shaped reinforcing member for reinforcing the protecting tube.
In the protecting tube, the reinforcing member may be buried in the protecting tube. The protecting tube may be a spirally corrugated tube, a smooth-walled tube, etc.
The transparent protecting tube for external cable may be formed from a resin material or a resin composition containing at least 30% by weight of an ionomer resin in which a part or whole of the carboxyl groups of an ethylene-unsaturated carboxylic acid copolymer have been neutralized with metal ions or ammonium ions.
In addition, the present invention includes a resin material or a resin composition for use in a transparent protecting tube for external cable. The resin material or the resin composition contains at least 30% by weight of an ionomer resin in which a part or whole of the carboxyl groups of an ethylene-unsaturated carboxylic acid copolymer have been neutralized with metal ions or ammonium ions.